Portable stool



FIG. 1 is a perspective view of a portable stool.

FIG. 2 is a front elevation view of the portable stool.

FIG. 3 is a first side elevation view of the portable stool.

FIG. 4 is a rear elevation view of the portable stool.

FIG. 5 is a second elevation view of the portable stool opposite the first side elevation view; and,

FIG. 6 is a top plan view of the portable stool.

The broken lines shown in the drawings depict environmental features that form no part of the claimed design. 

CLAIM I claim the ornamental design for a portable stool, as shown and described. 